1. OBJECTIVES, FUNCTIONS, TYPES AND ECONOMICS OF MAINTENANCE
The objectives of maintenance are to ensure the desired plant availability at an optimum cost within the safety prescription. In otherwords, it may be mentioned that the objective of maintenance is to minimise the total cost of unavailability and resources. Whenever the plant is not available either due to breakdowns or due to planned stoppages, the following costs are incurred.
1) Loss of earnings due to stoppage of equipment
2) Loss of in service materials.
In addition the following costs are incurred on resources:
1) Labour of overhead expenses
2) Materials in spares and consumables
3) Cost of storage of spares and facilities.
Hence, maintenance functions are so, organised as to minimise the total cost of unavailability and resources.
The above mentioned objectives are attained by taking certain action illustrated below: Action
Return or slow down the process
of deterioration or wear
d. Application of
e. Examination of the Assess the extent of wear and
state of the
determine, on that basis, the
action required to check a
break-down and the time when
f. Analysis of history
such action should be taken
of behaviour of the
machine and its
g. Replacement of worn
h. Repair of cracks or
Restore the original operational capacity of the machine
and prevent further damage
i. Modification of design
of the components or
location of the
Affect improvements to reduce
the frequency of attention or
to reduce cost of maintaining
j. Capital replacement
Replacement of the machine when
the age of the existing machine
requirements of quality and
quantity of output and
emergence of better machines
make it economical to dislodge
the present and install a new
In these, the first four steps are taken with the sole purpose of reducing friction, wear and effects of environment on the individual parts of a machine. For example, lubrication reduces friction; cleaning prevents corrosion and abrasion due to dust; adjustment of level or alignments or by tightening the loose bolts and nuts eliminates undue stresses; and preventive coatings guard against rust and corrosion. These action increase the useful life of parts and therefore, constitute an intrinsic part of Preventive Maintenance.
The next two steps, inspection of parts and analysis of history, are meant to assess the condition of the part, the extent of wear, the action required to remedy the defect and the time when such action should be undertaken. These activities are undertaken essentially to be able to plan the remedial measures.
Inspection can be external for abnormal sound or temperature which does not require a stoppage of the machine. It could even be internal, requiring a machine to be stopped either purely for inspection or at the time of some other repair or during overhauling of the machine. Historical data on the other hand, is a chronological record of repairs and replacements carried out on a machine during its life in the company. Analysis of such a record helps to estimate the life span of various components and establish the frequency of inspections, repairs, and replacements. Replacement and repair of components can be undertaken on the basis of inspection reports, analysis of history or complaints of operating personnel.
Another important part of maintenance is the change in some characteristics of the components which gives frequent trouble, to avoid re-occurrence of that trouble with that frequency. Such an action is taken on the basis of history of the equipment and evaluation of costs involved. This
maintenance engineering and management
step can be defined as "Maintenance Prevention". Cost of maintenance...
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